Jumbo Red Sardonyx Agate 16mm Barrel Beads - Heavy!Price is for per 16 inch string of these beautiful beads ready for stringing. Each bead measures a large 16mm x 16mm. No gemstone is more creatively striped by nature than agate, technically, chalcedony quartz that forms in concentric layers in a wide variety of colours and textures. Each individual agate forms by filling a cavity in its host rock, resulting in round nodules, with bands like the rings of a tree trunk, looking like eyes. Agate was